1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to golf balls having a core and a cover, with dimples formed on the cover.
2. Description of the Related Art
General golf balls have a core and a cover. There exist the cores composed of a single solid rubber layer, those composed of two or more solid rubber layers, those composed of a solid rubber layer and a synthetic resin layer, and the like. Dimples are formed on the surface of the cover.
Flight performances are important to golf balls. In light of the flight performance, a variety of disposals have been made with respect to shape of the dimples. U.S. Pat. No. 5,735,757 discloses a golf ball having double radius dimples with a predetermined shape. U.S. Pat. No. 6,346,053 discloses a golf ball with edge angle and curvature radius set to fall within a predetermined range.
Density of dimples (referred to as “occupation ratio”) also affects the flight performance. Golf balls having a great occupation ratio are excellent in the flight performance. U.S. Pat. No. 4,813,677 discloses a golf ball having dimples densely arranged such that any novel dimple having an area that is greater than the average area can not be formed.
Spin performances are also important to golf balls. Great back spin rate results in small run (a distance from the fall point of a golf ball to the point where it stopped). For golf players, golf balls which are liable to be spun backwards are apt to be rendered to stop at a target point. When side spin rate is great, the golf ball is liable to curve. For golf players, golf balls which are liable to be side spun are apt to be rendered to intentionally curve. Golf balls that are excellent in spin performances are excellent in control performances. Senior golf players particularly place great importance on control performances upon impact with a short iron. JP-A-2002-191721 discloses a golf ball having an improved control performance through using a soft polyurethane elastomer for the cover.
At the impact between a golf ball and a golf club, the surface of the golf ball is scuffed by the face line of the golf club. Nap is thereby raised on the surface of the golf ball. Thus resulting nap markedly deteriorates the appearance of the golf ball. Force is liable to converge in the vicinity of the edge of a dimple, where the nap is readily raised. The nap shall remain along the contour of the dimple.
According to golf balls having a great occupation ratio of the dimples, area of the land shall be small. The place where a golf club comes into contact upon impact is a land. Because golf balls having a great occupation ratio have a small substantial contact area upon impact, a great force is applied against the land. According to golf balls with a great occupation ratio Y, raising of the nap is liable to be caused. There is an urgent need to suppress deterioration of the appearance resulting from the nap, in golf balls having a great occupation ratio.
Physical strength of a polyurethane elastomer is great. Covers in which this polyurethane elastomer is used are excellent in a scuff resistance performance. Although use of the polyurethane elastomer may suppress the raising of the nap to some extent, such suppression is not sufficient. Because the polyurethane elastomer is inferior in resilience performances, to employ this polyurethane elastomer is disadvantageous in light of the flight performance.
An object of the present invention is to provide a golf ball that is excellent in a flight performance, a scuff resistance performance and a control performance.